This invention relates to hydraulic dampers and, particularly to hydraulic dampers of the type including a cylinder receiving hydraulic liquid therein, a piston working in the cylinder and partitioning the interior of the cylinder into two chambers, a piston rod secured to the piston and extending through one of the two chambers to the outside of the damper, an axial bore extending through the piston rod, an elongated adjusting rod axially displaceably disposed in the bore of the piston rod with the inner end thereof cooperating with an orifice member which is mounted on the inner end of the piston rod, and a passage defined by the axial bore in the piston rod for connecting the two chambers through a radial bore in the piston rod which opens to the one chamber and through an orifice of the orifice member which opens to the other chamber.
The adjusting rod can be operated from the outside of the damper whereby the liquid flow passing through the passage can be adjusted. Conventionally, a valve mechanism is incorporated in the piston, and the liquid flow flowing through the passage in the piston rod acts as a by-pass flow against the oil flow through the valve mechanism whereby the damping force of the damper can be adjusted by operating the adjusting rod from the outside of the damper.
A hydraulic damper of the type aforementioned is disclosed in Japanese Utility Model Publication No. 53-26550 and Japanese Utility Model Disclosure (Kokai) No. 50-85962.
However, there are shortcomings in the prior art hydraulic dampers of the type aforementioned in that, due to manufacturing tolerances with respect to the length of the piston rod and the adjusting rod, the configuration of the orifice member and the adjusting rod, and the location of the orifice member with respect to the piston rod, it is very difficult to properly locate the adjusting rod with respect to the orifice member, and in that it is difficult to suitably determine the range of the adjustment on the damping force with respect to the range of the vertical displacement of the adjusting rod.
Conventionally, an actuating or adjusting mechanism is mounted on the piston rod for operating the adjusting rod from the outside. In such case, the stroke of the adjusting mechanism is required to correspond with the stroke of the adjusting rod such that the adjusting rod can reliably displace with respect to the orifice member between a minimum flow or the zero flow condition and a predetermined maximum flow condition in response to the stroke of the adjusting mechanism. Otherwise, the adjusting rod would be deformed in receiving excessive force from the adjusting mechanism, or a desired range of adjustment can not be attained.